An outraged crowd has tried to storm a US consulate in western Afghanistan. Altogether 12 people have been killed and scores wounded on the fourth and bloodiest day of violent protests over the burning of the Korans at Bagram airbase.

Three people died as 500 protesters surged towards the US consulate in the city of Herat.In northeastern Baghlan province protesters tried to overrun the Czech-led military-civilian reconstruction team. While in the eastern province of Khost protesters have set fire to 20 NATO trucks.

Also on Friday hundreds of demonstrators descended on the presidential palace in Kabul. A crowd of angry protesters threw stones at police and chanted "Death to America!" and "Long live Islam!" after they left the city's Blue Mosque following Friday prayers.

A 700-strong crowd also gathered in the eastern city of Jalalabad and the volatile southeastern province of Ghazni. Demonstrators chanted "We will defend the Koran!"

US embassy officials in Kabul have urged calm through their Twitter feed. "I call on everyone…to exercise patience and restraint as we continue to gather the facts surrounding Sunday night’s incident," US embassy Twitter quoted General John R. Allen, who is in command of the International Security Assistance Force(ISAF) and of US Forces Afghanistan (USFOR-A).

AFP Photo/Shah Marai

AFP Photo/Shah Marai

AFP Photo/Shah Marai

AFP Photo/ Shah Marai

On Thursday, Barack Obama apologized for the incident which took place at Bagram base on Sunday. He sent an official letter of apology to President Karzai. "I convey my deepest sympathies and ask you and the people to accept my deepest apologies,” the letter read. NATO officials also made their apologies immediately after the incident, but this did not prevent riots breaking out the country.

On the same day, the Taliban urged Afghans to attack Western military bases in retaliation. Al-Qaeda has echoed the Taliban’s calls, telling its followers to target military hubs and kill Westerners following the desecration of the Muslim sacred book, a crime that carries the death penalty in Afghanistan.

US officials claim the texts seized from arrested Afghans were burned unintentionally. Gen. John Allen, commander of NATO's International Security Assistance Force, told media the texts had been confiscated from a detainee center's library as they seemed to have "extremist inscriptions" on some of the pages. US troops suspected that those books were being used in order to “facilitate extremist communications."

Gen. Allen stressed that the materials were gathered for disposal and inadvertently given to troops for burning.

Meanwhile, Lebanese group Hezbollah said the Koran burning incident was the result of strong Israeli influence on the US.

"We should search for the Israeli mentality that stands behind various practices in the world. Take for example the burning of Korans,” Hezbollah chief Sayyed Hasan Nasrallah said Friday.